Thermal fluid heater

ABSTRACT

A method of heating or cooling a heat transfer fluid prior to circulation through a heat exchange system wherein the heat transfer liquid is circulated helically through an elongated substantially unobstructed annular chamber. The helical flow is caused by the angle and position of entry of the fluid into the vessel. The swirling fluid is exposed to suitable heating or cooling means to transfer heat with the fluid.

United States Patent [1 1 Palm et al.

[ July 24, 1973 THERMAL FLUID HEATER [75] Inventors: Lewis J. Palm; Ronald B. Palm, both 2/1972 Waeselynck 165/1 HEAT SOURCE Kohl 165/155 Neumann et al. 165/155 Primary Examiner-Charles Sukalo Attorney-E. Manning Giles and J. Patrick Cagney [57] ABSTRACT A method of heating or cooling a heat transfer fluid prior to circulation through a heat exchange system wherein the heat transfer liquid is circulated helically through an elongated substantially unobstructed annular chamber. The helical flow is caused by the angle and position of entry of the fluid into the vessel. The swirling fluid is exposed to suitable heating or cooling means to transfer heat with the fluid.

8 Claims, 8 Drawing Figures THERMAL FLUID HEATER BACKGROUND AND SUMMARY OF THE INVENTION This invention relates to a method of heating or cooling thermal fluids for use in heat exchange systems. These systems operate by heating or cooling a fluid in a central location, i.e., in a heater or in refrigeration equipment'and then moving the fluid through pipes to a point where the heat or cold of the fluid is utilized to perform a heat exchange function.

The method disclosed is particularly advantageous for use in systems'where high pressure is not desirable. Examples of such uses are heating reactors and distillation columns, industrial drying, and heating platens and molds in a plastic molding operation. At these high temperatures the use of water and steam requires the maintenance of a highly-pressurized system because of the low boiling point of water. The use of water or steam is impractical under these conditions for economic reasons since the equipment must be constructed to reflect the high pressure requirements. Therefore, it is of particular advantage to use liquids having a high boiling point such as mineral oils; diphenyl diphenyloxide mixtures; chlorinated biphenyls; silicones, silates and silanes; polyglycols;and polyphenyl ethers and esters.

It is conventional to heat these thermal fluids in heaters of the coil or tube type. Such heaters include. a myriad of tubes or coils located in a heat transfer vessel. In the conventional tube or coil type heater, thermal fluid enters a tube bundle and passes through these tubes which are in contact with the heat or flame. The fluid is heated as it moves through the coil. The tubes and coils in a heater of this type tend to restrict theflow of the fluid, such restriction results in overheating at certain points and inefficiency in heat transfer resulting from the uneven-heating. Further inefficiency results because tube heaters cannot maximize the contact of heat transfer fluid with the heatingmeans.

Tube-type heaters also presenta maintenance problem because of the tendency of the tubes to burn out. Such heaters are also difficult to clean because of the irregular tube surfaces. I

In accordance with the'present invention, the thermal fluid enters a substantially unobstructed annular heat transfer vessel with a spinning or helical flow caused by its angle and position of entry into the vessel, this helical flow iscarefully maintained as fluid moves through the vessel. The fluid vessel can be either verti- The heating system disclosed in the present invention is of the type having a tubeless or coilless construction.

This system has a greater thermal efficiency and allows a more even flow of fluid than a tub'eor coil heater. The thermal fluid passes through the tubless annular heat transfer vessel which is designed to receive heat from the heating medium in such a way that the continuous helical flow of the fluid is not impaired.

[none embodiment of the invention disclosed herein,

the heating medium is-circulated both" through the inner opening of the annular vessel and over the exterior shell of the vessel. In this manner, the medium makes a two-pass heating contact with the annular vessel. The two-pass heating contact takes maximum advantage of the heating ability of the medium used. The heating action of the two-pass system on the swirling fluid gives both an efficient and even heat transfer from the heating medium to the thermal fluid.

Other features and advantages of the invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which show structure embodying preferred features of the present invention and the principles thereof, and what is now considered to be the best mode in which to apply these principles.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings forming a part of the specification, and in which like numerals are employed to designate like parts throughout the same:

FIG. 1 is a system diagram showing the heater unit operatively connected to the various external components that complete a practical operating embodiment.

FIG. 2is a fragmentary perspective view showing the flow relationships occurring within the heater.

FIG. 2A is a transverse sectional of the perspective of FIG. 2.

FIG. 3 is a transverse sectionalview through the heater, better showing its physical arrangement and, in particular, showing the tangential entry path of the thermal fluid. t

FIG. 4 is an elevational view of another embodiment of this invention.

FIG. 4A is a top plan view of the embodiment of FIG. 4.

FIG. 5 is a fragmentary perspective view of another embodiment of this invention, and FIG. 6 is a top vie of same.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the system shown generally in FIG. 1, thermal fluids, particularly liquids other than water, such as, mineral oils; diphenyl-diphenyloxide mixtures; chlorinated biphenyls; silicones, silates and silanes; polyglycols; and polyphenyl ethers and esters are pumped by a circulating pump 10 into a fluid vessel 11. This vessel is made of heat conductive material and consists of an inner annular shell 12 concentric with and surrounded by an outer annular shell 13. The outer shell 13 is of larger diameter than the inner shell 12, therefore, a space or path is defined through which the fluid is to flow. The cold fluid enters the fluid vessel through an inlet 14 placed at the bottom of the vessel 11. The pressure created bythe circulating pump 10 forces the fluid to flow upward through the annular vessel until it reaches a fluid outlet 15 at the top of the vessel. The thermal fluid is heated to the desired temperature as it passes through the annular vessel.

The annular fluid vessel 11 is contained within the heating unit 16. The unit includes an outer steel jacket 17 and an inner steel jacket 18 with an insulation layer 19 between them. There is a space left-between the inner jacket 18 and the outer annular shell 13 of the heat transfer vessel 11. The fluid vessel is attached to 'the base of the heating unit by angle supports 20 (only one shown). Heat is transferred to the moving fluid by hot gases ignited at the top of the heating unit 16.

Air is taken in through the inlets 21 in ablower assembly 22 and mixed with a gaseous ignition fuel in the burner assembly 23. The mixture is deflected downward through the air blast tube 24 and the funnel shaped air deflector 25. After passing the deflector 25,

the gas-air mixture is ignited and combusts in the'inner annular shell 12 of the heating vessel 11. The burner assembly 23 shown in FIG. 1 is located at the top of the heating unit 16; alternative constructions would be to locate the burner at the bottom or in the middle of the unit.

a As the hot blend goes downward through the interior of the inner annular shell 12, it gives up some of its heat into the shell. The hot gases are forced downward under the vessel 11.

As shown in FIG. 1, and in greater detail in FIG. 3, the hot gas after passing under the fluid vessel travels upward through a secondary flue pass. The secondary flue pass consists of the annular opening between the external shell 13 of the fluid vessel 11 and the inner jacket 18 of the insulation layer 19. Equally spaced vertical ribsor fins 26 are joined to the circumference of the outer shell 13 of the fluidvessel 11. These ribs or fins 26 are effective in absorbing the heat from the gases rising through the secondary pass. The hot gases pass up through the secondary flue and gives their remaining heat'into the conductive outer annular shell 13 of the fluid vessel 11. Therefore, both. sides of the fluid vessel are heated. The upward rising hot gases or products of-combustion leave the system through a flue outlet. When the heated fluid reaches the top of the fluid vessel, it is forced through an outlet 15 into the external heating system. l

The heated thermal fluid isvcirculated to the external system and then is recirculated from the external systemthrough the pump and inlet 14 after it performs its heating function. A pressure indicator and pressure fluctuation reliever 28 is provided on the return path of the fluid to the heating unit.

\ In accordance with the present invention, as shown in FIGS. 2 and 2A, improved efficiency and evenness of heat exchange are produced by the flow relationships occurring within the heater. The thermal fluid to be heated is pumped into the annular fluid heating -vessel 11 through an inlet 14 which is tangential to the fluid flow path defined by the annular vessel 11 and at a 90 angle to the vertical axis of the annular vessel. This tangential entry path causes the thermal fluid to come into and flow through the fluid vessel with a spinning or swirling motion. The entire volume of fluid rotates and mixes around the vessel. The fluid is therefore induced to spin around and between the annular shells I2, 13 of the fluid vessel 11 in a helical path. To heat the fluid, the burner assembly gives a circular or whirling movement to the gaseous heat exchange medium as it passes downwardly of-the interior of the inner annular shell 12 ofthe heating vessel 11. The circular movement of the gas plus thenatural tendency for heat to rise, slows the downward movement of the flame; thereby, efficiently heating the inner annular shell 12. When the hot gas reaches the bottom of the interior of the annular heating vessel, it turns upward to make a complete second pass around the exterior of the outer shell of the heating vessel, thereby, transmitting additional heat to the outer annular shell and consequently to the fluid. The flow relationship shown in FIGS. 2 and 2A produces maximum heat transfer because of the smoothness of flow of the thermal fluid through the annular path and also because of the length of flow through the vessel caused by the rotational movement. This ideal fluid flow is exposed to double pass heat which takes maximum advantage of the heating ability of the gaseous medium.

The design of the heating vessel is ideal for heating thermal fluids due to the even distribution of two-pass heat and the minimal restriction of the moving fluid. The minimal restriction of the fluid in the heating vessel results in a low pressure drop. The annular vessel can be constructed with the following dimensions depending on the heating system required: 1) length of the vessel, 24 inches to 96 inches; 2) outer diameter of the vessel, 12 inches to 48 inches; 3) distance between the inner and outer walls of the vessel, 1 inch to 10 inches; and 4) inlet diameter, l'/a inches to 3 inches.

The flow rate of the fluid is controllable through the vessel, and as such is dependent upon the distance between the inner and outer walls of the vessel. In addition, the flow rate must be kept above a minimum level in order to keep the thermal fluid from burning or scorching. This heater will operate at a minimum flow rate of 1 foot per second and can be adjusted to a maximum of 10 or 15 feet per second. This feature allows the thermal fluid heater to be used for a wide variety of applications.

The construction shown in FIGS. 4 and 4A makes use of multiple inlets and outlets. Five inlets 30, 31, 32, 33, 34 are shown all feeding fluid into a tangentialpath for helical flow. As shown in FIGS. 4 and-4A, the fluid inlets can be placed at locations other than the bottom of the heating vessel. This construction uses two outlets 35, 36 to send heated fluid into the system.

A further embodiment of this invention is illustrated in FIG. 5. In this embodiment thermal fluids of the type previously described are pumped into a fluid vessel 40.

This vessel consists of an inner annular shell 41 concentric with and surrounded by an outer annularshell 42 so that a space or path is defined through which the fluid is to flow. Cold fluid enters the fluid vessel through an inlet 43 placed at the bottom of the vessel 40. Fluid is forced to flow upward of the vessel by pressure created by a circulating pump (not shown). The thermal fluid is heated to the desired temperature as it passes through the annular vessel. The fluid vessel 40 is contained within a heating unit and is circulated to the external system substantially, as described in conjunction with the previous embodiment. I-Ieat is transferred to the moving fluid by thin electrical resistance elements 44 extending vertically the length of the vessel.

These resistance elements are grouped in sets of five, each set 45 forming a resistance heating zone. Four'sets of elements are arranged equally spaced apart from each other. These sets of elements each create an elevated temperature zone within the annular vessel 40.

As in the previously described embodiment, the thermal fluid to be heated is pumped into the annular fluid heating vessel 40 through an inlet 43 which is tangential to the fluid flow path defined by the annular vessel 40 and at a 90 angle to the vertical axis of the vessel.

The tangential entry path causes the thermal fluid to come into and flow, through the fluid vessel 40 with a spinning or swirling motion and causes the entire vol- The resistance elements are constructed out of g of water along .a substantially axially unobstructed elongated annular chamber that is bounded by inner and outer chamber walls that encircle a central axis,

said method comprising the steps of:

producing in a closed system a continuous bodily flow of said liquid continuously swirling about the central axisin a path of predetermined width and characterized by rotary and axial flow components cooperatively determining a flow that continuously fills and sweeps the entire chamber by introducing adjacent one end of the chamber a stream of said liquid along a direction that is tangent to the cham- 6 ber periphery; conduction heat through the chamber walls to said liquid as it sweeps said annular chamber; and withdrawing the liquid from adjacent the other end. 2. A method as in claim 1 wherein said liquid continuously swirls about the central axis in a path of one inch width.

3. A method as in claim 1 wherein said liquid continuously swirls about-the central axis in a path of 10 inches width.

4. A method as in claim 1 wherein said bodily flow is in a vertical direction and said thermal liquid is introduced adjacent the lower end of the chamber and with drawn adjacent the upper end.

-5. A method as in claim 1 wherein said liquid is withdrawn at ,a temperature in excess of 250 F.

6. A method as in claim 1 wherein said heat is conducted to said fluid by a heating medium circulating in teriorly and exteriorly of said fluid flow path.

7. A method as in claim 6 wherein said heating medium is circulated interiorly of said fluid flow path in a direction opposite that of the axial flow direction of the thermal liquid, then continues its circulation in a return direction exteriorly of said fluid flow path.

8. A method as in claim 4 wherein heat is conducted to said fluid by introducing a heating medium interiorly of the upper end of said fluid flow path, circulating said medium downwardly interior of said path, circulating under the path, then circulating said medium upwardly exterior of said path and withdrawing said heating medium exteriorly of the upper end of said fluid flow path. 

1. A method of indirectly exchanging heat with a thermal liquid having a boiling point higher than that of water along a substantially axially unobstructed elongated annular chamber that is bounded by inner and outer chamber walls that encircle a central axis, said method comprising the steps of: producing in a closed system a continuous bodily flow of said liquid continuously swirling about the centrAl axis in a path of predetermined width and characterized by rotary and axial flow components cooperatively determining a flow that continuously fills and sweeps the entire chamber by introducing adjacent one end of the chamber a stream of said liquid along a direction that is tangent to the chamber periphery; conduction heat through the chamber walls to said liquid as it sweeps said annular chamber; and withdrawing the liquid from adjacent the other end.
 2. A method as in claim 1 wherein said liquid continuously swirls about the central axis in a path of one inch width.
 3. A method as in claim 1 wherein said liquid continuously swirls about the central axis in a path of 10 inches width.
 4. A method as in claim 1 wherein said bodily flow is in a vertical direction and said thermal liquid is introduced adjacent the lower end of the chamber and withdrawn adjacent the upper end.
 5. A method as in claim 1 wherein said liquid is withdrawn at a temperature in excess of 250* F.
 6. A method as in claim 1 wherein said heat is conducted to said fluid by a heating medium circulating interiorly and exteriorly of said fluid flow path.
 7. A method as in claim 6 wherein said heating medium is circulated interiorly of said fluid flow path in a direction opposite that of the axial flow direction of the thermal liquid, then continues its circulation in a return direction exteriorly of said fluid flow path.
 8. A method as in claim 4 wherein heat is conducted to said fluid by introducing a heating medium interiorly of the upper end of said fluid flow path, circulating said medium downwardly interior of said path, circulating under the path, then circulating said medium upwardly exterior of said path and withdrawing said heating medium exteriorly of the upper end of said fluid flow path. 